Hydrocarbon conversion process



Dec. 22, 1959 J. V. D. FEAR ET AL HYDROCARBON CONVERSION PROCESS Filed Jan. 14, 1957 nus l 5 nus 8 Q o g "3 1 fi d5 .ISMOJ, QIHHODA w \I A JOJDUOHODJA INVENTORJ'. JAMES v. D. FEAR FRANK R.SHUMAN AT ORNEY Un ed State aw Q 2,918,423 iiYDR'ocARBoN CONVERSION PROCESS Jim Van Dyck Fear, Media, and Frank R. Shiiman, ."Jr Chester Springs, Pa., assignors to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application January 14, 1957, Serial No. 633,937

2 Claims. c1. 208--96) invention relates to a process for the conversion of hydrocarbons, and more particularly to an improved catalytic cracking process in which a high grade recycle gascil and a fraction suitable for the production of lubricating oil are produced.

' lrr one commercial process, described in US. Patent 2,616,836 to Schmidt et a1. a fresh gas oil, in admixture with a recycle gas oil obtained from a later stage is passed to a reactor inwhich it is catalytically cracked. The reaction products are then sent to a fractionating column from which a gasoline fraction is recovered overhead; a furnace oil fraction is taken oif as a side stream near the re of the column; a gas oil fraction is taken ofi as a side stream near the bottom of the column, and a bottoms product. is recovered from thebottom of the col- The gas oil is subjected to solvent extraction, in order to remove refractory aromatics, and the rafiinate recycled to admixture with fresh feed to the cracking step. While this patent shows recycling of the bottoms product to the cracker, this fraction contains components of lubricating value, so that, when facilities are available, it is more economically advantageous to process this fraction by solvent extraction to recover lubricating oil as a raffinate, and a good quality carbon black oil as an extract. As may be observed, when proceeding according to Schmidt, it is necessary to solvent extract all the gas oil recycled to the process.

The present invention is an improvement over Schmidt, in that by proceeding in the manner hereinafter set forth, it is possible to prepare a recycle gas oil of excellent cracking quality without the necessity of extracting all of the gas oil recycled. In addition, a greater quantity of lubricating oil may be recovered than when proceeding according to the prior art.

In accordance with the present invention, a mixture of fresh and recycle gas oil is taken to a catalytic cracker and is therein cracked in a conventional manner. The cracked products are then taken to a products fractionator in which they are separated into an overhead fraction boiling through gasoline, a light fuel side stream, a gas oil side stream, and a bottoms fraction. Instead of taking off a full boiling range gas oil, having a boiling range say of 5% off at 580 F. to 95% over at 750 F., as in the prior art, the fractionator is controlled to limit the 95% point of the gas oil to about 720 F., thus throwing a considerable portion of the gas oil down into the bottoms. It has been found that by so limiting the boiling range of the gas oil side stream, a product is recovered which contains so little coke-forming compounds that extraction is unnecessary, and this stream may be directly recycled to admixture with fresh feed to the cracker.

The bottoms from the products fractionator are then passed to a vacuum tower in which a fraction having an end point (corrected to 1 atm.) of about 700 F. is taken overhead, a gas oil fraction having a boiling range from about 650 F. to about 760 F., and preferably from 650 F. to 720 F., is taken off as a side stream, and a bottoms product is recovered which has a 5% over boil ing point of at least about 720 F. The overhead fraction contains very little refractory material, so that it is recycled to admixture with the fresh gas oil feed to the cracker. The side stream, which normally comprises about 40% of the cracked product boiling in the gas oil range, contains the bulk of the gas oil coke-forming material. This fraction is sent to a solvent extraction unit in which it is contacted with a selective solvent in order to separate it into a parafiinic raffinate, which is re cycled to form a part of the feed to the cracker, and an extract which may be disposed of as fuel or as a carbon black oil.

p The bottoms from the vacuum tower which contains over of hydrocarbons boiling in the lubricating oil range may be further processed as by solvent extraction to recover a paraffinic raflinate which can be dewaxed to produce a high V.I., unusually oxidation stable lubricating oil.

Inorder that those skilled in the art may more fully understand the nature of our invention and the manner of carrying it out, a specific example will be hereinafter described in connection with the drawing, which is a diagrammatic flow sheet of our new process.

Fresh gas oil is taken from storage through line 1, is mixed with recycle gas oil from line 2, and is passed to reactor 3 in which the mixed feed is catalytically cracked. The cracked products are then sent through line 4 to fractionator 5, in which material boiling in the gasoline boiling range and below is taken overhead through line 6 for further processing into uncondensible gases, L.P.G., and gasoline. A No. 2 fuel oil fraction is taken off as a side stream through line 7, near the top of fractionator 5, a gas oil stream is taken off through line 8, and a bottoms fraction is removed through line 9. In a conventional operation, when charging 35,000 b./d. of feed to a Houdriflow cracker, 8200 b./d. of gas oil having a boiling range (Engler) of 5% over at 583 F., 50% over at 676 F., and over at 745 F., would be removed through line 8. Since a gas oil of this boiling range contains sufficient coke forming compounds to make it undesirable as a cracking stock according to Schmidt it is normally sent to a solvent extraction plant invwhich the refractory components of the fraction are removed, the rafiinate from the solvent extraction being recycled to reactor 3.

Similarly, in a conventional operation, the bottoms removed from fractionator 5 will consist of 2800 b./ d. of an oil having a boiling range (Engler) of 5% over at 664 F., 30% over at 745 F., and 95% over at 900 F. As may be observed, there is a considerable overlap between the boiling ranges of the side stream and the bottoms, but this is inevitable in any commercial fractionation of a highly complex mixture, in which one of the product streams is a side stream removed from the frac tionator at a point not far from the bottom thereof. The bottoms could be used as feed to a lubricating oil plant, but since about 30% of the bottoms boils below the lubricating oil range, only about 1,960 b./ d. is available as a lube oil feed.

In accordance with the present invention, however, only 3,300 b./d. of a gas oil fraction having a boiling range (Engler) of 5% over at 530 F., 50% at 635 F., and 95% at 680 F. is taken off through line 8. This fraction contains insufficient coke-forming compounds to make it undesirable as a cracking stock, so that it may be recycled directly to reactor 3 via line 2. 7700 b./d. of hottoms is withdrawn through line 9 and is taken to vacuum tower 10 which is controlled to take overhead 1000 b./ d. of a cracking stock having an end point of 700 F through line 11 for direct recycle through line 2 to reactor 3. 3700 b./d. of a gas oil side stream having a 3 boiling range of 5% over at 670 F., 50% at 706 F., and 95% at 750 F. is taken off through line No. 12, and 3000 b./d. of bottoms having a 5% point of 720 F. is recovered through line 13.

Theg as oil side stream in line 12 is taken to solvent extraction unit 14 in which it is contacted with a solvent selective for aromatics such as furfural. A raftiniate phase is recovered from solvent extraction unit 14 through line 15 and is taken to still 16 from which solvent is removed overhead through line 17 for recycle to solvent extraction unit, while a clean cracking stock is removed as bottoms and recycled to reactor 3 via lines 18 and 2. An extract phase is removed from extraction unit 14 through line 19, and is passed to still 20, from which solvent is recovered overhead through line 21 for recycle to unit 14 and an aromatic-rich hydrocarbon fraction is recovered as bottoms through line 22.

As may be observed from the foregoing, by proceeding according to the present invention, it is possible to reduce the amount of gas oil which must be extracted to 3700 b./d. as compared to the 8200 b./d. which must be extracted in a conventional process. In addition, since the bottoms from vacuum tower contain 95% of material boiling in the lubricating oil range- (over 720 F.) the amount of material available for the manufacture of lubricating oil has been increased to 2850 b./d. as compared to the 1,960 b./d. available from a conventional process. While the amount of lubricating oil stock is increased, the amount of gas oil recycle stock available is not correspondingly decreased, since relatively non-coke-forming compounds are left in the streams flowing through lines 8 and 11, which aromatics would have been extracted and lost to the process if the entire gas oil recycle had been subjected to solvent extraction, as in conventional processes.

While in the foregoing description vacuum tower 10 was controlled to take off an overhead fraction for direct recycle to the cracker, and a side stream for further processing ina solvent extraction unit, it is within the scope of our invention to dispense with the side stream, and to take overhead all the material recovered through lines 11 and 12. This combined fraction would then be solvent extracted. The scheme illustrated in the drawing is pre- 4 a ferred, however, since the size of the extraction unit may be kept to a minimum, and the heat load on the vacuum tower is lessened.

We claim:

1. A catalytic cracking process comprising passing feed comprising fresh gas oil in admixture with recycle gas oil recovered in a later stage of the process to a reactor, catalytically cracking the feed therein, recovering cracked products, fractionating the products to recover a first fraction boiling in the gas oil range and having a over point of not over 720 F., and a higher boiling fraction, recycling said first fraction to admixture with the feed to the reactor, fractionating said higher boiling fraction to recover a second fraction boiling from'about 650 F. to about 760 F. and a bottoms fraction having a 5% over boiling point of at least 720 F., contacting said second fraction with a solvent selective for aromatics, recovering a raffinate phase, removing solvent from the rafiinate phase to obtain a rafiinate and recycling the rafiinate to admixture with the feed to the reactor.

2. A catalytic cracking process comprising passing a feed comprising fresh gas oil in admixture with recycle gas oil recovered in a later stage'of the process to a reactor, catalytically cracking the feed therein, recovering cracked products, fractionating the products to recover a first fraction boiling in the gas oil range and having a 95% over point of not over 720 F., and a higher boiling fraction, recycling said first fraction to admixture with the feed to the reactor fractionating said higher boiling fraction to recover an overhead fraction having an end boiling point of not more than 720 F., a side stream boiling from about 650 F. to about 760 F., and a bottom fraction having a 5% over boiling point of at least 720 F., contacting said side stream with a solvent selective for aromatics, recovering a rafiinate phase, removing solvent from the ratfinate phase to obtain a ratfinate and recycling the rafiinate and the overhead fraction to admixture with the feed to the reactor.

References Cited in the file of this patent UNITED STATES PATENTS; 

1. A CATALYTIC CRACKING PROCESS COMPRISING PASSING FEED COMPRISING FRESH GAS OIL IN ADMIXTURE WITH RECYCLE GAS OIL RECOVERED IN A LATER STAGE OF THE PROCESS TO A REACTOR, CATALYTICALLY CRACKING THE FEED THEREIN, RECOVERING CRACKED PRODUCTS, FRACTIONATING THE PRODUCTS TO RECOVER A FIRST FRACTION BOILING IN THE GAS OIL RANGE AND HAVING A 95% OVER POINT OF NOT OVER 720*F., AND A HIGHER BOILING FRACTION, RECYCLING SAID FIRST FRACTION TO ADMIXTURE WITH THE FEED TO THE REACTOR, FRACTIONATING SAID HIGHER BOILING FRACTION TO RECOVER A SECOND FRACTION BOILING FROM ABOUT 650*F. TO ABOUT 790*F. AND A BOTTOMS FRACTION HAVING A 5% OVER BOILING POINT IF AT LEAST 750*F., CONTACTING SAID SECOND FRACTION WITH A SOLVENT FOR AROMATICS, RECOVERING A RAFFINATE AND RECYCLING THE RAFFINATE PHASE TO OBTAIN A RAFFINATE AND RECYCLING THE RAFFINATE TO ADMIXTURE WITH THE FEED TO THE REACTOR. 